The TPM_IO_Hash_Start() function can be used by an implementation of the TPM TIS hardware interface to indicate the beginning of a hash operation. Following the TPM TIS interface specification it resets several PCRs and terminates existing transport sessions. The TPM_IO_Hash_Data() function is used to send the data to be hashed to the TPM. The TPM_IO_Hash_End() function calculates the final hash and stores it in the locality 4 PCR. The 3 functions must be called in the order they were explained.

The implementation of the above functions handles all TPM-internal actions such as the setting and clearing of permanent flags and PCRs and the calculation of the hash. Any functionality related to the TPM's TIS interface and the handling of flags, locality and state has to be implemented by the caller.